Welding is where fabrication quotes go wrong most often, and quietly. A fillet weld is a single line on a drawing, but behind that line sit a dozen cost variables — joint geometry, plate thickness, number of passes, prep, position, and the cleanup nobody bills for. Estimators who price machining down to the tenth of a minute will wave a hand at "say two hours of welding" and lose the margin on the whole job. This guide breaks down welding cost estimation into the parts you can actually measure, so your fabrication cost estimate rests on numbers instead of gut feel.

The aim is to know, for any weldment, three things: how much weld metal you have to deposit, how long the arc and the welder have to be working to deposit it, and what the prep, consumables, and finishing add on top. Get those right and how to quote welding jobs stops being guesswork.

What actually drives welding cost

A weld's cost is driven less by its length than by its cross-section. The two together give you the volume of deposited metal, and that volume sets both arc time and filler consumption.

• Joint type. A fillet weld on a T-joint or lap joint deposits a triangular bead and usually needs no edge preparation. A butt weld joining two plates edge-to-edge often needs a bevel (V, double-V, or J prep) and far more weld metal as thickness grows. Corner joints and outside-corner welds fall in between.
• Material thickness. Thickness is the multiplier. A 6 mm plate butt weld might be one or two passes; a 20 mm plate needs a prepped groove and six to ten passes, each one arc time you pay for. Fillet leg size scales the same way — weld metal grows with the square of the leg length, so an 8 mm fillet carries roughly 1.7× the metal of a 6 mm one.
• Weld length and weight. Total deposited weld weight is the single best driver for both time and filler. For a fillet, weld metal per metre ≈ (leg² ⁄ 2) × 7.85 g/cm³ × reinforcement factor. Sum it across every weld on the part and you have the basis for the whole estimate.
• Material and process. Stainless and aluminium are slower and dearer than mild steel — different filler, different gas, more cleaning, tighter heat control. MIG/MAG deposits faster than stick; submerged arc faster still.

How to estimate weld time

Arc time is the deposited weight divided by the deposition rate of your process. Manual MMA (stick) sits around 1–2 kg/hr, MIG/MAG around 2–5 kg/hr, flux-cored higher, submerged arc much higher. So 0.5 kg of weld metal at a 2.5 kg/hr deposition rate is about 12 minutes of arc-on time.

The trap is stopping there. A welder is not arcing for every minute they are on the clock. Operating factor (arc-on time as a share of paid time) for manual work is typically 20–40% — the rest goes to repositioning, changing wire, chipping slag, checking fit, and resting. Divide arc time by your real operating factor to get billable welder time. That 12-minute arc job is realistically 30–40 minutes of paid labour.

Then add the time that has nothing to do with the arc: joint preparation (bevelling, cleaning to bright metal), fit-up and tacking, and travel speed limits where a single pass on thin material is governed by how fast the welder can move without burn-through, not by deposition rate. Estimate each as its own line; bundling them into a vague "weld time" is how shops underquote.

Consumables: filler, gas, and electricity

Consumables rarely break a quote on their own, but on long runs they add up and they are easy to forget entirely.

• Filler wire or rod. Priced per kg. You deposit slightly more than the joint volume — budget 5–15% loss to spatter, stub ends, and stick-out. Stainless and aluminium filler can cost several times mild-steel wire.
• Shielding gas. CO₂ is cheapest, an Ar/CO₂ mix (commonly 80/20) is standard for MAG on steel, and pure argon is used for MIG on aluminium and for TIG. Gas cost is flow rate (typically 10–18 L/min) times arc time — plus the gas wasted on pre-flow, post-flow, and draughts. A cylinder rental line belongs in overhead, not the part cost.
• Electricity, tips, and nozzles. Small per-part, but real on volume. Contact tips, nozzles, and grinding discs are genuine per-job consumables on long contracts.

The prep and post-weld work that gets underquoted

Most welding quotes are wrong not at the arc but on either side of it.

Before the weld: cutting and profiling (saw, plasma, laser), edge bevelling, deburring, grinding to clean metal, and fit-up. On a multi-part weldment, fit-up and jigging can exceed the welding itself. If the blanks come off your own machine, cost that step properly too — the laser cutting cost calculation guide builds the per-blank number from cut length, pierces, and gas.

After the weld: interpass and final cleaning, grinding welds flush where the drawing demands it, stress relief or post-weld heat treatment on thick or critical work, straightening, and inspection — from a quick visual to dye penetrant, magnetic particle, ultrasonic, or radiographic testing called out on the drawing. Then surface finishing: blasting, priming, painting, galvanising, or powder coating. Each of these is a real cost line, and any one of them can be larger than the weld.

The hidden hours

These are the line items that never make it onto a hand-written quote, and together they are often 30–50% of the real labour:

• Tack welding and fixturing — setting up jigs, clamps, and tacks to hold geometry.
• Distortion control and correction — pre-setting, back-stepping, and straightening after welding pulls the part.
• Repositioning and manipulation — flipping heavy weldments, crane time, working out of position.
• Cleaning — slag, spatter, and discolouration removal between passes and at the end.

If you do not name these, you will not price them. Put them on the estimate as explicit lines.

Time per metre by joint type

A practical starting table for manual MIG/MAG on mild steel, including a realistic operating factor. Treat these as defaults to calibrate against your own logged times, not as gospel.

Joint type	Typical size	Passes	Weld metal (kg/m)	Est. time per metre
Fillet weld	3–4 mm leg	1	0.05–0.08	6–10 min
Fillet weld	6 mm leg	1	0.13–0.18	10–15 min
Fillet weld	8–10 mm leg	2–3	0.25–0.45	18–30 min
Butt weld (single-V)	6 mm plate	1–2	0.20–0.30	15–25 min
Butt weld (single-V)	12 mm plate	3–4	0.55–0.80	35–55 min
Butt weld (double-V)	20 mm plate	6–8+	1.2–1.8	70–110 min

Multiply the per-metre time by your fully burdened welder-hour rate, add prep, consumables, and finishing, and you have a defensible weld line.

How AI drawing interpretation scopes the weld

The slowest part of quoting a weldment by hand is reading the drawing: finding every weld symbol, decoding the fillet leg or groove size, the length, whether it is all-round or intermittent, field-weld flags, and the finishing notes. Miss one symbol on a busy drawing and the whole estimate is short.

AI drawing interpretation reads the technical drawing and surfaces the weld scope for you — it flags the weld symbols, calls out joint types and sizes, and lists the welds so nothing is silently dropped. It does not decide your price. The deterministic estimator does that, applying your deposition rates, operating factor, welder rate, consumable costs, and markup the same way every time, so two estimators quoting the same weldment land on the same number. The AI handles the reading; your rules handle the pricing.

That split is exactly how QuoteBuddy works for fabrication and welding shops. You set your weld-time assumptions, material and consumable costs, and markup once, and every interpreted drawing gets the same consistent treatment — RFQ to quote PDF in minutes instead of an afternoon. See the plans and pricing to start a 30-day trial, or read more shop-floor guides on the blog.